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Commit 301084de authored by Or Cohen's avatar Or Cohen Committed by Greg Kroah-Hartman
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net/sctp: fix race condition in sctp_destroy_sock 



commit b166a20b07382b8bc1dcee2a448715c9c2c81b5b upstream.

If sctp_destroy_sock is called without sock_net(sk)->sctp.addr_wq_lock
held and sp->do_auto_asconf is true, then an element is removed
from the auto_asconf_splist without any proper locking.

This can happen in the following functions:
1. In sctp_accept, if sctp_sock_migrate fails.
2. In inet_create or inet6_create, if there is a bpf program
   attached to BPF_CGROUP_INET_SOCK_CREATE which denies
   creation of the sctp socket.

The bug is fixed by acquiring addr_wq_lock in sctp_destroy_sock
instead of sctp_close.

This addresses CVE-2021-23133.

Reported-by: default avatarOr Cohen <orcohen@paloaltonetworks.com>
Reviewed-by: default avatarXin Long <lucien.xin@gmail.com>
Fixes: 61023658 ("bpf: Add new cgroup attach type to enable sock modifications")
Signed-off-by: default avatarOr Cohen <orcohen@paloaltonetworks.com>
Acked-by: default avatarMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2965db2e

net/sctp/socket.c

+5 −8
Original line number Diff line number Diff line
@@ -1569,11 +1569,9 @@ static void sctp_close(struct sock *sk, long timeout) 


	/* Supposedly, no process has access to the socket, but

	 * the net layers still may.

	 * Also, sctp_destroy_sock() needs to be called with addr_wq_lock

	 * held and that should be grabbed before socket lock.

	 */

	spin_lock_bh(&net->sctp.addr_wq_lock);

	bh_lock_sock_nested(sk);

	local_bh_disable();

	bh_lock_sock(sk);



	/* Hold the sock, since sk_common_release() will put sock_put()

	 * and we have just a little more cleanup.
@@ -1582,7 +1580,7 @@ static void sctp_close(struct sock *sk, long timeout) 
	sk_common_release(sk);



	bh_unlock_sock(sk);

	spin_unlock_bh(&net->sctp.addr_wq_lock);

	local_bh_enable();



	sock_put(sk);
@@ -4776,9 +4774,6 @@ static int sctp_init_sock(struct sock *sk) 
	sk_sockets_allocated_inc(sk);

	sock_prot_inuse_add(net, sk->sk_prot, 1);



	/* Nothing can fail after this block, otherwise

	 * sctp_destroy_sock() will be called without addr_wq_lock held

	 */

	if (net->sctp.default_auto_asconf) {

		spin_lock(&sock_net(sk)->sctp.addr_wq_lock);

		list_add_tail(&sp->auto_asconf_list,
@@ -4813,7 +4808,9 @@ static void sctp_destroy_sock(struct sock *sk) 


	if (sp->do_auto_asconf) {

		sp->do_auto_asconf = 0;

		spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);

		list_del(&sp->auto_asconf_list);

		spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);

	}

	sctp_endpoint_free(sp->ep);

	local_bh_disable();